Sound recording



Oct. 31, 1933. D MOORE 1,932,982

SOUND RECORDING Filed Dec. 15, 1932 INVENTOR Patented Oct. 31, 1933 SOUND RECORDING David Pelton Moore, Avon Park, Fla., assignor to General Talking Pictures Corporation, New York, N. Y., a corporation of Delaware Application December 15, 1932 Serial No. 647,443

6 Claims.

The present invention relates to improvements in sound recording and more particularly to recording sound-on-film to produce what isknown in common parlance as noiseless recording, one object of the invention being the provision of an arrangement of glowlamp recording in which the present type of glow lamp recording system' variable density type and by and in accordance with the sound to be recorded.

A further object of this invention is the. provision of a sound recorder in which a novel arrangement of galvanometer control is used in conjunction or in coordination with arecording lamp of the photion or glow type so that :1 normal luminosity of the lamp ismaintained at all times and the lamp in the same close proximity as is the practice in recording systems of this type at the present time, the galvanometer control means being so arranged that it is influenced due to the impinging of sound waves upon the micro phone and simultaneously with the modulation of the glow lamp so as to permit the rays of light from the glow lamp during the sound modulation thereof, to affect the moving sensitized film, thus producing an automatically controlled means which when the microphone is not having sound waves impinged thereon will cause a light excluding barrierto be interposed between the lamp and the film so that the sensitized film as a nega: tive when developed will have an entirely clear sound track, and which when barrier is open will permit the proper recording thereon in the usual manner. 1

With the ioregoingand other objects in, view, which will appear as the description proceeds, the invention resides in the combination and arrangement of parts and in the details of construction hereinafter described'and claimed, it being understood that changes in theprecise embodiment of the invention 'hereindisclosed can be made within the scope of what is claimed without departing from the spirit of the invention.

Although several circuits may be employed to accomplish this result, there is illustrated and described in this particular case only one form but such form is clearly illustrative of the present invention. g

In the accompanying drawing:

Figure 1 is a diagrammatic view of a complete recording installation embodying the present invention. v p

Figure 2 is a diagrammatic view of an iris diaphragm shutters g Figure 3 is a view of a modified form of shutter which displacesthe iris diaphragm. g u

Referring to the drawing, and more'particular- 1y to Figures 1 and 2 thereof, the numeral 1 designates a microphone which is connected in the usual manner through conductors 2 and 3 to a. first stage amplifier 4, which in turn is connected by conductors 5 andsfi to a second stage amplifier 7. Conductors 8 and 9 connect the output of the'amplifier 7 to theinput oi a power amplifier 10, the output of which is connected to; the glower recording lamp 11' through conductors 12 and 12, a stepping condenser 13 beingin terposed therein. A conductor 12" is connected 75, to conductor 12 and hasa variable resistance 14. Conductors 15 and 17 are connected to the negative side of the battery 18 jand theamplifier l0,

conductors 19 and 19' beingconnected to the lamp 11 at the opposite side of the battery 18. This much less. the conductor 12 and variable resistance 14 constitutes in general a normal sound recording system. A galvanometer G'is connected by conductor 19" to elementsl4 14 at one side and at the other side to the battery 18 through the conductor 19. A coupling resist, ance 20 is employed as usual and with the variable resistance 14 controls the amount of direct current through the galvanometer. Conductors 21 and 22 are connected to the conductors 8 and 9 respectively and to an auxiliary power amplifier 23, the output of which is connected through the conductors 24 and 25, to a Wheatstone bridge rectifier network apparatus 26 with the stopping. condenser 27 in the line. The power amplifier 23 is here shown in the form of an output'transformer, the terminals ofithe secondaryof which are connected to the points 28 and 29 of the network 26 whose remaining points .30 and 31 are connected respectively through the conductors 32 and 33 to the conductors 15' and 17 respectively. Connected inthe line 32' and 33 and be-.- tween the lines 32 and 33 is a large reservoir condenser 16 there being provided a ground connection at 27 and also a ground connection at 20. A by-pass condenser 14 is also provided around the resistance 14. i v

This, galvanometer as shown in Figure 2 is op erably connected to thearmeoof the iris diaphragm shutter 41 and as will presently-appear,

when no sound is impinged upon the microphone will hold the shutter in closed position, but instantly upon the impinging of sound upon the microphone will be moved to open position so that the rays of light from the terminals 42, 42 of the lamp 11 will be pe'rmittedto-pass through the slit 43 andthus affect the sensitized film 44. This film as is usual in recording apparatus is carried by the respective supply reel 45 and take-up reel anism or sprockets 4'7 and 48. a

By this arrangement it will be noted that ther is introduced in series with'th'e galvanometer and the main supply battery'18 an additional-source 15 of direct current, that is, through the medium of the large reservoir condenser 16. This is maintained charged at a fixed and desired polarity by means of the special rectifying network 26, the latter as shown consisting primarily of four rectifiers 36, 3'7, 38 and..39,arranged as indicated, and in suchamannerthat the current fromthe output ofnthetransformer 23 is delivered at the terminals 30 and 31 of the network and always flows -inthesame direction, regardless v of the rever- 25 sals of the voltage across the input terminals 28 and 29.. Thus, by. this bridged rectifier circuit arrangement theoutput energy from the amplifier 23,15 at alltimesistored inthe large reservoir cone denser. 1'6 .withunchanging polaritybut in vary- 30 inglamounts at varyi'ngpotential's. Thus, by the above circuit arrangement there is secured a variable additional source of F. in series with thebattery m, the amount of additional voltage being therebyintroduced into the galvanometer supplycircuit' and is. proportional to the amount ofenergy coming from the auxiliary amplifier 23' whichin' turnis proportional to the amount 0t sound. energy ,picked' up. by the microphone.

Thuswhen no soundv isimpressed upon the 40 microphone 1 the normal current passing through thegalvanometer. .willhaverbeen such as ,to cause.

the'shutter 41Ztobeheld in. closedposition while thetcathode .42 of .thelamp 11 will be at all times @q subjectto the same current effects, and as the 45 microphoneis not beingimpinged by soundits rays are shut ofithroughthe shutter 41 so as to be inefi'ectivetupon. the film. The impingement of.

the sound upon. the" microphone however will causethegalvanometer. to be sufficiently energizedtoopen the shutter 41 .and thuspermit the modulated-light'rays from the lamp 11 to impinge upon the moving film 44 and thus effect the same, so that, when developed, a variable density sound. track will. result. with. interspersed even dense spaces..

It will thus be evident-that'with this-system the negative filmwhen developed will containthe sound track thereonin which thesilent intervals due .totheabsolute'closure of the shutter '41 will be.substantiallytransparent and will therefore print upon the positive when developed a constant or even black which when run through a soundv reproducing machine will have no percenibl'e ground noise and to all intents and purposes will produce silence where intended.

Thusth'ereis addedto the normal photion or glowlamp recording system an auxiliary device which renders'theeffect of the lamp 'upon the film negative'during periods of silence, or when the microphone is notbeing impinged, by sound, but instantly upon the'impingement of sound upon the microphone will permit the rays of light from the photion or glow lamp to be recorded on the filn'r by and in-"a'ccordance with the sound to be 7 recorded.

46 and is operated by the film progressing mech- By means of. the auxiliary voltage supply circuit here shown and described and in which the voltage is supplied from the auxiliary amplifier 23 an additional amount of current is passed through the galvanometer but only when sounds above a certainthreshold of intensity are being delivered to the microphone. During all such intervals, therefore, the galvanometer is actuated to maintain the shutter 41 open. The instant,

however, that the sounds delivered to the record .ing microphone cease or fall below a certain definite threshold value, no additional energy from the power amplifier or transformer 23 is delivered to the largereservoircondenser 16, and as soon as the existing change in said condenser has cleared itself from the circuit, which it does by tailing oif through the galvanometer circuit, and also including the resistance 14 and 20, the

galvanometer returns to a normal state and closes the galvanometer G may operate a blade shut-' ter 18, the galvanometer being connected through a' lever 49 to the shutter 48 so as to positively oscillate the same across the slit 43 in a-positive manner.

Various types of mechanism for operating the shutter may be employed, suchfor instance as a spring in combination with the galvanometer, orany sensitive electric motor, it being essential however that the galvanometer or operating mechanism be so adjusted that the shutter is open the instant that sound is impinged upon the microphone, and closed the instant of the cessation thereof.

From the foregoing description taken in" connection with the drawing, it is. evident from this arrangement that the recording lamp may be actuated in its usual manner with the'glow end thereof at the proper relative distance from the film, and that the sound recording operation thereof is controlled in the usual manner while an auxiliary means is introduced and controlled through the action of the microphone so as to render the effect of the lamp upon the film effective or ineffective to produce what is known as "nois'eless recording.

What is claimedis:

1; A sound-on-filni recording apparatus including" in combination a film advancing means, means for directing a light beam to the film, a microphone; an amplifier the input of which is connected to the microphone, a power amplifier, the input of which is connected to the output of the amplifier, a second power amplifier connected to the output 'of the first amplifier, a sound modulated recording lampconnected to the output of the first power'amplifier, a rectifying network composed wholly of rectifying elements and connected to the output of the second power amplifier, a shutter interposed between the recording lamp and the means for directing the light beam to the film, an electrical device operably connected to the shutter, a source of electrical energy connected to the output of the first amplifier and also to the output of the network;

and supplementing current source means mantained charged by means of the network whereby the output energy of the second power amplifier is at all times stored with current of unchanging polarity but in varying amounts at varying potentials, and whereby the shutter actuating electrical device is operated to hold the shutter closed when no sound is impinged upon the microphone, but to instantly open the same when sound is impinged upon the microphone.

2. A sound-on-film recording apparatus as claimed in claim 1 wherein the electrical device is a galvanometer.

3.. A sound-on-film recording apparatus as claimed in claim 1 wherein the electrical device is a galvanometer and the supplementing cur rent source means is a reservoir condenserr i. A sound-on-film recording apparatus as claimed in claim 1 wherein the electrical device is a galvanometer and the supplementing current source means is a reservoir condenser and the rectifying network is a Wheatstone bridge.

5. A sound-on-film recording apparatus including in combination a film advancing means, a fixed slitted barrier by means of which light is permitted upon a limited area of the film during tie advancing thereof, a microphone, a first and second amplifier operably connected to the microphone, a first power amplifier connected to the output of the second amplifier, a sound modulated recording lamp adjacent the slitted barrier and operably connected to the output of the first power amplifier and the circuit thereto including a main source ofelectrical energy and a condenser, a galvanometer also connected to the output of the first amplifier and to the main source of energy and including in its circuit a condenser and a variable resistance, a second power amplifi er in the form of a transformer connected to the output of the second amplifier, a Wheatstone bridge connected to the output of the transformer and having in circuit therewith a reservoir condenser, the latter of which is connected to the main electrical source of energy to constitute a supplementing current source means which is maintained charged by the Wheatstone bridge so that the output energy of the transformer is at all times stored with current of unchanging polarity but in varying amounts at varying potentials, and a shutter operablyconnected to the galvanometer to be interposed between the recording lamp and the slit of the slitted barrier whereby the same acts as a barrier to cut off the light from the recording lamp to the film when no sound is being impinged upon the microphone, and

which is moved and held to open position during the impinging of sound upon the microphone.

6. A sound-on-film recording apparatus as claimed in claim 1, wherein the rectifying network is a Wheatstone bridge wherein the supplementing current source means is a reservoir condenser and wherein the electrical device includes mud 

